The proposed project is designed to explore the physiological requirements for the initial interaction of platelets with collagen. The studies will be done using the technique of affinity chromatography on columns of collagen/Sepharose. Measurements will be made of changes in cyclic AMP occurring with platelet adherence to collagen. The effect on platelet-collagen adherence of agents which alter the cellular levels of cyclic AMP and cyclic GMP will be studied. In addition, studies will be done of the effect on this interation of agents that affect sulfhydryl groups, contractility, and prostaglandin and thromboxane synthesis. The results should increase our understanding of the factors affecting this initial event in hemostasis and thrombosis.